Traditional fabrics have, for centuries, been decorated and had their surface texture modified by embroidery and other needle arts. Originally, this process was obtained through tedious hand labor, painstakingly applying fine stitches that had the cumulative effect of building up a region of the background fabric according to some particular pattern. The resulting product had a base fabric, comprised of threads or yarns, woven or knitted according to some pattern, a raised region formed by a collection of threads in some stitch pattern, and an overall pattern of these raised regions determined by their respective size, shape, orientation and placement. While rich in appearance, these products were complicated to create and costly to produce.
Most nonwoven fabrics are flat and visually uninteresting. In some instances, nonwoven fabrics are embossed or printed with some sort of design to provide visual interest. In other instances, nonwoven fabrics are provided with an integral pattern during the course of their manufacture. Those having an integral pattern of their own fall into two categories:
1) Apertured fabricsxe2x80x94where a pattern is created by a network of bundled fiber segments surrounding apertures or holes; or
2) Weight patterned fabricsxe2x80x94fabrics that achieve a visual effect by concentrating fibers into regions of higher basis weight to increase opacity relative to the lower basis weight regions which are more translucent.
It is important to differentiate between basis weight and density. xe2x80x9cBasis weightxe2x80x9d is the weight of a unit area of fibrous web or fabric or portion thereof being characterized. Basis weight has also been called xe2x80x9carea densityxe2x80x9d in some prior art patents. The term xe2x80x9cdensityxe2x80x9d is the weight of a unit volume of a fibrous web or fabric or portion thereof being characterized. xe2x80x9cDensityxe2x80x9d has also been called xe2x80x9cVolume densityxe2x80x9d in some prior art patents. Typical embossing processes create regions of higher density without altering the basis weight. Traditional nonwoven patterning processes produce regions of varying basis weight, while maintaining substantially uniform density.
The prior art nonwoven fabrics made with these known patterning processes do not have clear, well defined raised portions and therefore the desired patterns are difficult to see. In addition, the raised portions of prior art embossed nonwoven fabrics are not dimensionally stable and their raised portions lose their three-dimensional structure when stressed, as for example, when they are handled or laundered.
The present invention is directed to nonwoven fabrics having a fibrous background portion in one plane thereof and raised fibrous portions in another plane thereof. There may be two types of raised portions. The basis weight of the first type of raised portion is substantially the same as the basis weight of the background portion of the nonwoven fabric. The basis weight of the second type of raised portion is greater than the basis weight of the background portion.
In accordance with a first embodiment of the present invention, there is provided a nonwoven fabric comprising a background portion and at least one raised portion. The background portion is located in and defines a first plane of the nonwoven fabric. The raised portion of the nonwoven fabric is located in a second plane which is above and parallel to the fast plane. The raised portion is joined to the background portion by a fibrous transition region. In this specific embodiment the basis weight of the raised portion is substantially the same as the basis weight of the background portion. The density of the background portion and the density of the raised portion are substantially the same. A raised portion whose basis weight is substantially the same as the basis weight of the background portion is sometimes referred to as an xe2x80x9cintaglioxe2x80x9d portion.
In accordance with a second embodiment of the present invention there is provided a nonwoven fabric which also comprises a background portion and at least one raised portion. As was the case with the first embodiment, the background portion is located in and defines a first plane of the nonwoven fabric and the raised portion is located in a second plane which is above and parallel to the first plane. As was the case with the first embodiment, the raised portion is joined to the background portion by a fibrous transition region. In the case of the second embodiment however, the basis weight of the raised portion is greater than the basis weight of the background portion. The density of the raised portion of this nonwoven fabric is substantially the same as the density of the background portion. A raised portion whose basis weight is greater than the basis weight of the background portion is sometimes referred to as a xe2x80x9cslubxe2x80x9d portion.
In a third embodiment of the present invention, there is provided a nonwoven fabric comprising a background portion, at least one first raised portion, and at least one second raised portion. As was the case with the first and second embodiments discussed above, the background portion is located in and defines a first plane of the nonwoven fabric. The first raised portion is located in a plane which is above and parallel to the first plane. Similarly the second raised portion is located in a plane which is above and parallel to the first plane. Each of the first and second raised portions is joined to the background portion by a fibrous transition region. In this embodiment, the basis weight of the first raised portion is substantially the same as the basis weight of the background portion, while the basis weight of the second raised portion is greater than the basis weight of the background portion. In other words, in this embodiment, the nonwoven fabric has one or more first raised portions which are sometimes referred to as xe2x80x9cintaglioxe2x80x9d portions and one or more second raised portions which are sometimes referred to as xe2x80x9cslubxe2x80x9d portions. In this embodiment, it is not necessary that the first raised portion and the second raised portion be in the same plane; rather the first raised portion may be in a plane which is above the plane of the background portion and the second raised portion may be in a plane which is above the plane of the first raised portion.
In the process of forming nonwoven fabrics of the present invention, a web or layer of fibers or a lightly entangled fibrous web is placed on a foraminous forming plate or topographical support member comprising an essentially planar background surface with at least one relatively wide recessed region significantly displaced from the background surface of the forming plate. Typically the support member comprises a multiplicity of recessed regions, positioned as depressions in some predetermined way, that will form a desired pattern of raised portions on the nonwoven fabric. Fluid forces, in the form of streams of water, are applied to the upper surface of the starting fibrous web or layer of fibers. Initially, these fluid forces xe2x80x9cmoldxe2x80x9d the starting web to the three dimensional support member; as the process of applying fluid faces continues, the fibers am entangled and locked together so as to provide a nonwoven fabric comprising a background portion and one or more raised portions which are permanently positioned with respect to one another.
In an alternative embodiment, the topographical support member has a relatively narrow recessed region displaced from the planar background surface of the forming plate.